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Title: Infrared vibrational predissociation spectroscopy of water clusters by the crossed laser-molecular beam technique

Abstract

Water clusters formed in a molecular beam are predissociated by tunable, pulsed, infrared radiation in the frequency range 2900--3750 cm/sup -1/. Absorption spectra of the clusters are obtained by detecting the recoiling fragments off-axis from the molecular beam as a function of laser frequency using a rotatable mass spectrometer. By carefully adjusting the expansion conditions of the molecular beam and monitoring the largest cluster observable, excessive contamination by clusters larger than the specific one of interest is avoided. It is found that the spectra of clusters containing three or more water molecules absorb over the same frequency range as the liquid. Dynamical information on the predissociation process is obtained from the measured angular and velocity distributions of the fragments. An upper limit to the excited vibrational state lifetime of approx.1 ..mu..s is observed for the results reported here. The most probable dissociation process concentrates the available excess energy into the internal motions of the fragment molecules. From adiabatic dissociation trajectories and Monte Carlo simulations it is seen that the strong coupling present in the water polymers causes extensive energy sharing among the intermolecular motions in the polymer before dissociation, consistent with the experimentally measured energy distributions. Comparison between current intermolecularmore » potentials describing liquid water and the observed frequencies is made in the normal mode approximation. The inability of any potential to predict the gross spectral features (the number of bands and their observed frequency shift from the gas phase monomer) suggests that substantial improvement in the potential energy functions is possible, but that more accurate methods of solving the vibrational wave equation are necessary before a proper explanation of the spectral fine structure is possible.« less

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Materials and Molecular Research Division, Lawrence Berkeley Laboratory and Department of Chemistry, University of California, Berkeley, California 94720
OSTI Identifier:
5288104
Resource Type:
Journal Article
Journal Name:
J. Chem. Phys.; (United States)
Additional Journal Information:
Journal Volume: 77:1
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; WATER VAPOR; AGGLOMERATION; INFRARED SPECTRA; PREDISSOCIATION; ABSORPTION SPECTRA; LASER RADIATION; MOLECULAR BEAMS; VIBRATIONAL STATES; BEAMS; DISSOCIATION; ELECTROMAGNETIC RADIATION; ENERGY LEVELS; EXCITED STATES; FLUIDS; GASES; RADIATIONS; SPECTRA; VAPORS; 640302* - Atomic, Molecular & Chemical Physics- Atomic & Molecular Properties & Theory

Citation Formats

Vernon, M F, Krajnovich, D J, Kwok, H S, Lisy, J M, Shen, Y R, and Lee, Y T. Infrared vibrational predissociation spectroscopy of water clusters by the crossed laser-molecular beam technique. United States: N. p., 1982. Web. doi:10.1063/1.443631.
Vernon, M F, Krajnovich, D J, Kwok, H S, Lisy, J M, Shen, Y R, & Lee, Y T. Infrared vibrational predissociation spectroscopy of water clusters by the crossed laser-molecular beam technique. United States. doi:10.1063/1.443631.
Vernon, M F, Krajnovich, D J, Kwok, H S, Lisy, J M, Shen, Y R, and Lee, Y T. Thu . "Infrared vibrational predissociation spectroscopy of water clusters by the crossed laser-molecular beam technique". United States. doi:10.1063/1.443631.
@article{osti_5288104,
title = {Infrared vibrational predissociation spectroscopy of water clusters by the crossed laser-molecular beam technique},
author = {Vernon, M F and Krajnovich, D J and Kwok, H S and Lisy, J M and Shen, Y R and Lee, Y T},
abstractNote = {Water clusters formed in a molecular beam are predissociated by tunable, pulsed, infrared radiation in the frequency range 2900--3750 cm/sup -1/. Absorption spectra of the clusters are obtained by detecting the recoiling fragments off-axis from the molecular beam as a function of laser frequency using a rotatable mass spectrometer. By carefully adjusting the expansion conditions of the molecular beam and monitoring the largest cluster observable, excessive contamination by clusters larger than the specific one of interest is avoided. It is found that the spectra of clusters containing three or more water molecules absorb over the same frequency range as the liquid. Dynamical information on the predissociation process is obtained from the measured angular and velocity distributions of the fragments. An upper limit to the excited vibrational state lifetime of approx.1 ..mu..s is observed for the results reported here. The most probable dissociation process concentrates the available excess energy into the internal motions of the fragment molecules. From adiabatic dissociation trajectories and Monte Carlo simulations it is seen that the strong coupling present in the water polymers causes extensive energy sharing among the intermolecular motions in the polymer before dissociation, consistent with the experimentally measured energy distributions. Comparison between current intermolecular potentials describing liquid water and the observed frequencies is made in the normal mode approximation. The inability of any potential to predict the gross spectral features (the number of bands and their observed frequency shift from the gas phase monomer) suggests that substantial improvement in the potential energy functions is possible, but that more accurate methods of solving the vibrational wave equation are necessary before a proper explanation of the spectral fine structure is possible.},
doi = {10.1063/1.443631},
journal = {J. Chem. Phys.; (United States)},
number = ,
volume = 77:1,
place = {United States},
year = {1982},
month = {7}
}